In plants, carotenoids act as accessory pigments in light harvesting, and more importantly, to detoxify various forms of activated oxygen and triplet state chlorophyll that are produced as a result of the excitation of photosynthetic complexes by light.
The dollar value of fruit and vegetable crops are dependent on freshness and quality. In the agricultural product handling and food processing industry, there is currently no precise method of determining fruit and vegetable quality or antioxidant nutrient content which is rapid enough to be useful in a continuous flow environment. The current quality control method for fruit and vegetable handlers typically consists of an expensive and imprecise manual selection process based on the color or shape of the product. An automated quality control process would be very useful.
In the food product industry, carotenoid levels (usually lycopene or beta-carotene) are determined using high-performance liquid chromatography (HPLC). These measurements are made throughout the food processing line to assure quality control of the final product. The delay in obtaining HPLC data, which is not a real-time process, leads to difficulties in identifying problems as they occur. A rapid and objective measurement of post-harvest fruit and vegetable quality would have several commercial applications within the agricultural product handling and food processing industries, especially with an increased interest in nutritionally specific claims for fruits and vegetables, and processed functional foods.
An improved system to monitor the health status of food crops has broad commercial potential in agricultural crop management. Traditional methods of determining crop stress (observation of wilting, change in coloration, etc.) appear after damage has already occurred, and crop yields may not be recoverable. Currently, chemical analysis using HPLC is one of the few means available to get early indications that a plant or crop is under stress. However, this technique is invasive, requiring a sample of plant matter for analysis. HPLC is also expensive, time-consuming, requires user training, and is inconvenient to perform away from a laboratory. Conventionally, plant samples may be taken to an analysis laboratory, adding time and expense to the analysis. The link between measurement and plant sample location also has to be recorded for later interpretation of results. Ambiguous results from an HPLC may result from a variety of factors, such as plant sample contamination, and are then inconvenient to repeat. The present invention allows non-invasive determination of stress and environmental effects on plant health, allowing crop yields to be increased. Hence, a system allowing automated quality control using a rapid or effectively instantaneous analysis technique would be extremely useful.
In U.S. Pat. No. 5,873,831, Bernstein et al. describe a system for measurement of carotenoid levels within the macula and fovea of the eye. However, the characterization of plants is not described.
In U.S. Pat. No. 6,052,187, Krishnan describes a plant analyzer based on fluorescence. In U.S. Pat. No. 5,576,550, Koppikar describes a phytoluminometer using luminescence techniques. In U.S. Pat. No. 6,114,683 to Spiering, a plant chlorophyll content imager is disclosed. However, the use and advantages of Raman scattering are not disclosed in these disclosures.
In U.S. Pat. No. 5,257,085, Ulich et al. discloses a Raman imaging lidar system. However, this system is restricted to short pulses of laser radiation and imaging applications. The identification of carotenoids is not disclosed.